According to The Sun, the pair joined the fellow Spice Girls Emma Bunton and Mel C for rehearsals for their upcoming reunion tour.
While the pair are not seen in the same image, it's clear that they were not standing too far apart.
The new photos come after Mel B (also known as Melanie Brown) alleged in an interview with Piers Morgan that she and Horner — formerly Geri Halliwell — once had a sexual encounter.
"Did you or didn't you with Geri Halliwell...did you sleep with her?" Morgan asked, to which Mel B replied, "Yeah, we all slept in a bed together but not 'like that' all of us."
"Did you sleep with Geri 'like that'? Piers then further inquired.
The 43-year-old singer responded, "She's going to hate me for this because she's all posh in her country house and her husband. But it's a fact. It just happened and we just giggled at it and that was it."
"It was just that once," Brown went on to say. "And hopefully when Geri gets asked that, which hopefully she will after this, she won't deny it. Because it was just a fun thing."
Horner has since denied Brown's recollection of the events, issuing a statement through her representation that read, "It has been very disappointing to read about all these rumours again, especially on Mother's Day of all days. She would like you to know that what has been reported recently is simply not true and has been very hurtful to her family."
Brown has not rescinded her claims, but she did reveal that she and Horner have spoken to one another at length, explaining, "I did the interview, but I just texted her and said: 'I admitted on Piers that we had a little bit of a thing but don't worry about it, it was all tongue in cheek and I didn't go into detail.' "
"I said: 'This was pre your husband, pre your baby, pre one of my babies. It's fine.' I don't know why everyone's making such a big deal about it," she continued.
"We had a long conversation," Brown added. "She texted me the night of [the interview] and then we spoke at length today - amongst other things cos we're getting ready for tour right now."
The upcoming Spice World - 2019 tour is scheduled to begin on May 24 in Dublin, Ireland. It will conclude on June 15 in London, England.