Mapping two dataset fields in to one tablix in SSRS

//Mapping two dataset fields in to one tablix in SSRS

//Dataset - dataset1(Value1,Value2,Value3)
Dataset - dataset2(Value1,Value4)

SSRS design
Tablix (parent dataset- Dataset1)

//Requirement - In same tablix need to map dataset2 fields.

//Below Expression
=lookup(Field!Value1.Value,Fields!Value1.value,Fields!Value4.value,"Dataset2")