Query to count sibling rows given ID of one SQL Server 2012

if I have a table, Tasks with the following sample rows

ID  ParentID    Status
1   101     Pending
2   101     Complete
3   101     Complete
4   102     Complete

Given ID =2, how can I get number of tasks not complete that belong to same parent? e.g.

Select Count(ID) from Tasks where Status <> ‘Complete’ and ID =2

above query does return correct results

Note, I do not want to do Select Count(ID) from Tasks where Status <> ‘Complete’ and ParentID=101 i.e. I do not want to pass parentID in query, just ID of one of the records that belong to same parent.

thanks.