The new couple was spotted spending Independence Day together, along with Donnie's fellow New Kids on the Block singer Jonathan Knight and his boyfriend, Harley.
"They recently started dating and are having a lot of fun," a source told Us. "They had a blast 4th of July hanging out with a bunch of their friends."
In late March, the "Blue Bloods" star, 43, was a guest on Jenny's VH1 late night talk show - and the chemistry between the pair was undeniable.
During one segment, Donnie and Jenny, 40, laid next to each other while sucking on red lollipops and dishing on bedroom chatter.
"Do you talk dirty when you're having sex?" Jenny asked Donnie, who smiled and replied, "I do."
"You do? But you know, some guys do it wrong," Jenny said.
"Yeah, but I don't do it wrong," he said with a laugh, as Jenny's eyes widened.
The blond bombshell later wrote about her interview with Donnie in a blog posted on Chicago Splash.
"I want to talk about what happened between Donnie Wahlberg and me. Let's just say we visually give '50 Shades of Grey' a run for its money. It gets steamy. I mean like really steamy," she wrote. "Being turned on by a guy is always fun but to have it legitimately happen to you on TV is to be turned back into a 12-year-old.
"By the time we get into the groundbreaking interview, my face turns fifty shades of RED," she continued. "If you were a New Kids On the Block fan back in the day, I totally get it. I think I have officially become a groupie."
Donnie has two sons from his marriage to Kim Fey, which ended in 2008.
Jenny has one son from a previous relationship.
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