Oooh this is interesting!
Leighton and Sebastian split up in April 2010, with reports doing the rounds that he didn't like being so public, and that she just didn't want to be in a relationship.
Then in February this year Dianna and Sebastian were rumoured to be getting close after her boyfriend at the time - Alex Pettyfer - allegedly picked a fight with Sebastian in a bar and accused him of hooking up with Dianna.
OH THE DRAMA.
Dianna and Sebastian are said to be taking things slow and trying to keep things to themselves.
"They're cute, Dianna is into Sebastian," a source tells US Weekly.
The two were also rumoured to be getting close last year, not too long after Sebastian and Leighton broke up with each other.
"He came to Dianna's 3pm Glee performance at the Staples Centre in Los Angeles on May 28th," said a source.
"He waited for her backstage. Once the cast finished the show Dianna ran backstage to Sebastian and they were all over each other!"
Ahh this all sounds very sweet.
Do you think Dianna and Sebastian would make a good couple? Would you like to see them do cameos in each other's shows?